1. Field of the Invention
The present invention relates to package structures and fabrication methods thereof, and more particularly, to a package structure having an MEMS (micro-electro-mechanical system) element and a fabrication method thereof.
2. Description of Related Art
MEMS elements have integrated electrical and mechanical functions and can be fabricated through various micro-fabrication technologies. A MEMS element can be disposed on a chip and covered by a shield or packaged with an underfill adhesive so as to form an MEMS package structure. There are various types of MEMS packages, such as metal packages, ceramic packages, thin film multi-layer packages, plastic packages and so on. To form a plastic package, an MEMS chip is disposed on a substrate and electrically connected to the substrate through bonding wires and then packaged with an encapsulant.
U.S. Pat. No. 6,809,412, No. 6,303,986, No. 7,368,808, No. 6,846,725 and No. 6,828,674 disclose MEMS packages.
FIGS. 1A to 1F are cross-sectional views showing a conventional fabrication method of a plastic MEMS package.
Referring to FIG. 1A, a wafer 10 having a plurality of conductive pads 101 and MEMS elements 102 is prepared.
Referring to FIG. 1B, a plurality of lids 11 are disposed on the wafer 10 to cover the MEMS elements 102, respectively, and each of the lids 11 has a metal layer 111 formed thereon.
Referring to FIG. 1C, the conductive pads 101 and the metal layers 111 are electrically connected through bonding wires 12. Then, an encapsulant 13 is formed on the wafer 10 to encapsulate the lids 11, the bonding wires 12, the conductive pads 101 and the metal layers 111.
Referring to FIG. 1D, portions of the encapsulant 13 and the bonding wires 12 are removed. As such, the bonding wires 12 are separated into first sub-wires 121 electrically connecting to the conductive pads 101 and second sub-wires 122 electrically connecting to the metal layer 111, and the top ends of the first sub-wires 121 and the second sub-wires 122 are exposed from the top surface of the encapsulant 13.
Referring to FIG. 1E, a plurality of circuits 14 are formed on the encapsulant 13 for electrically connecting the first sub-wires 121. Then, a plurality of bumps 15 are formed on the circuits 14, respectively.
Referring to FIG. 1F, a singulation process is performed to obtain a plurality of packages 1 having MEM elements 102.
However, in the process of forming the encapsulant 13 for encapsulating the lids 11, the bonding wires 12, the conductive pads 101 and the metal layers 111, mold flow of the encapsulant 13 can easily cause deviation of the positions of the bonding wires 12 and as a result, the positions of the exposed ends of the first sub-wires 121 are changed, thereby adversely affecting the electrical connection between the circuits 14 formed subsequently on the encapsulant 13 and the first sub-wires 121 and even causing failure of the electrical connection.
Therefore, it is imperative to provide a package structure having a MEMS element so as to overcome the above-described drawback.